Cell Structure Chapter 7

1. Cell StructureChapter 7 Section 1—Introduction to Cells Section 2—Inside the Eukaryotic Cell Section 3—From Cell to Organism

2. Introduction to Cells • Why it Matters • Cells are the basic unit of life. By studying cells, biologist can better understand life’s processes.

3. The Discovery of Cells • All life forms on our planet are made up of cells. The bacteria that live in our gut and the cells that make up our body are built from the same chemical machinery. • This machinery allows living things to obtain and use energy, to respond to their environment, and to reproduce. In all organisms, cells have the same basic structure.

4. Microscope observations of organisms led to the discovery of the basic characteristics common to all things. • In 1665, Robert Hooke, an English scientist, used a crude microscope to look at a thin slice of cork.

5. His microscope could only magnify objects up to 30 times their normal size. • Hooke saw many “little boxes” in the cork. They reminded him of small rooms so he called them cells.

6. Hooke later discovered cells in stems and roots of plants. • Ten years later, Anton van Leeuwenhoek, a Dutch scientist used a more powerful microscope that could magnify 300-fold. He discovered many loving creatures in pond water. He named them animalcules or tiny animals. • We know today that they were single-celled organism.

7. Euglena are single-celled organisms found in pond water.

8. Cell Theory • It took more than 150 years for scientist to fully appreciate the discoveries of Hooke and Leeuwenhoek. • In 1838, Matthias Scheiden, a German botanist conclude that cells make up every part of a plant. • A year later Theodor Schwann, a German zoologist, discovered that animals are also made up of cells. • In 1858 Rudolph Virchow, a German physician proposed that cells come from the division of existing cells.

9. The observations from Schleiden, Schwann, and Virchow form the cell theory. • The cell theory states: • All living things are made up of one or more cells. • Cells are the basic units of structure and function in organisms. • All cells arise from existing cells.

10. Looking at Cells • Cells vary greatly in size and in shape. • A cell’s shape reflects the cell’s function. • Cells can be branched, flat, round, or rectangular. Some have irregular shapes, while other cells constantly change shapes. • These differences enable different cells to perform highly specific functions in the body. • There are at least 200 types of cells. • The human body is made up of about 100 trillion cells.

11. Cell Size: • All substances that enter or leave a cell must pass through the surface of the cell. As a cell gets larger, it takes up more nutrients and releases more waste. • Cell size is limited by a cell’s surface area-to-volume ratio. • Cells with greater surface area-to-volume ratios can exchange substances more efficiently. • When cells are the same shape as one another are compared, the smaller cells have greater surface area-to-volume ratios than larger cells do.

12. Cell Shape: • Larger cells often have shapes that increase the surface are available for exchange. • A cell may grow large in one or two dimensions but remain small in others. • Examples: some skin cells are broad and flat. Some nerve cells are highly extended and can be more than 10,000 times as long as they are thick. In both of these types of cells, the surface area-to-volume ratio is larger that it would be if cells were spheres.

13. How does a cell’s size affect the cell’s function? • Smaller cells can exchange substances more efficiently than larger cells of the same shape can.

14. Cell Features • All cells share common structural features. • All cells have a cell membrane, cytoplasm, ribosomes, and DNA. • Cell membrane—is the cell’s outer boundary. It acts as a barrier between the outside environment and the inside of the cell. The cell membrane is a phospholipids layer that covers a cell’s surface and acts as a barrier between the inside of a cell and the cell’s environment.

15. The cytosol, the fluid inside the cell, is full of dissolved particles. • The cytoplasm includes the fluid and almost all of the structures that are suspended in the fluid. The cytoplasm is the region of the cell within the membrane. • Many ribosomes are found in the cytoplasm. • A ribosome is a cellular structure on which proteins are made. A ribosome is a cell organelle where protein synthesis occurs.

16. Features of Prokaryotic Cells: • A prokaryotic cell is a simple in its organization. It is a single-celled organism that does not have a nucleus or member-bound organelles. • Its genetic material is a single loop of DNA, which looks like a tangled string and usually lies near the center of the cell. Ribosomes and enzymes share the cytoplasm with the DNA.

17. Prokaryotic cells have a cell wall that surrounds the cell membrane and that provides structure and support. • Some are surrounded by a capsule and this structure allows them to cling to surfaces, including teeth, skin, and food. • For millions of years prokaryotes were the only organisms on Earth. • They live in a wide range of habitats. • They make up a very large and diverse group of cells.

19. Features of Eukaryotic Cells: • A eukaryote is an organism that is made up of one or more eukaryotic cells. • Some live a single cells and others are multicellular organisms. • All multicellular organisms are made up of eukaryotic cells . • Because of their complex organization, eukaryotic cells can carry out more specialized functions than prokaryotic cells can.

20. Primitive eukaryotic cells first appeared about 1.5 billion years ago. • A eukaryotic cell contains compartments that are separated by membranes. The cell’s DNA is housed in an internal compartment called the nucleus. • The nucleus is in a eukaryotic cell, a membrane-bound organelle that contains the cell’s DNA. • In addition to having a membrane, cytoplasm, ribosomes, and a nucleus, all eukaryotic cells have membrane-bound organelles.

21. An organelle is a structure that carries out specific activities inside the cell. • An organelle is one of the small bodies that are found in the cytoplasm of a cell and that are specialized to perform a specific function. • Each organelle perform distinct functions. • Many organelles are surrounded by a membrane. • Some membranes are connected by channels that help move substances within the cells.

24. Inside the Eukaryotic CellsSection 2 • Knowing how cells work helps you understand how your body functions and what goes wrong when you get sick.

25. The cytoplasm 0f a eukaryotic cell is packed with all sorts of structures and molecules. Many molecules can be concentrated in certain parts of the cell because of the membranes that divide the cytoplasm into compartments. This organization enables each organelle to perform highly sophisticated and specialized functions.

26. The Framework of the Cell • The cytoskeleton is a web of protein found in eukaryotic. It supports the cell in much the same way that bones support the body.

27. The cytoskeleton helps the cell move, keep its shape, and organize its parts. • There are three kinds of cytoskeleton fibers: • Microfilaments—are long thin fibers made of protein actin. They contract to pull the membrane in some places and expand to pull it out in others. • Microtubules—are thick hollow fibers that are made of protein tubulin. Information molecules move through these tubes to various parts of the cell. • Intermediate fibers—are moderately thick and mainly anchor organelles and enzymes to certain parts of the cell.

28. Directing Cellular Activity • Almost all cellular activity depends on the proteins that the cell makes. The instructions for making the proteins are stored in the DNA. In a eukaryotic cell, the DNA is packed into the nucleus. This location separates the DNA from the activity in the cytoplasm and helps protect the information from getting lost or destroyed.

29. Nucleus--it is surrounded by a double membrane called the nuclear envelope. • The nuclear envelope has many nuclear pores. • Nuclear pores are small channels that allow certain molecules to move in and out of the nucleus. • The DNA is very organized. • The nucleus has a prominent structure called the nucleolus. • It’s the region where ribosome parts are made. • These preassembled parts of the ribosomes pass through the nuclear pores into the cytoplasm. Outside the nucleus, the parts are assembled to form a complete ribosome.

30. Ribosomes—each ribosome is made of RNA and many proteins. • Some ribosomes in a eukaryotic cell are suspended in the cytosol, as they are in prokaryotic cells. These “free” ribosomes make proteins that remain inside the cell, such as proteins that build new organelles or enzymes to speed up chemical reactions. • Other ribosomes are attached to the membrane of another organelle. These “bound” ribosomes make proteins that are exported from the cell. • Some of these proteins are important in cell communication.

31. Bound ribosomes also make proteins that must be separate from the rest of the cytoplasm. • Ribosomes can switch from being bound or free depending on the kind of protein that the cell needs to makes. • What kind of proteins do “free” ribosomes make? • Proteins that remain in the cells, such as proteins that build new organelles or enzymes to speed chemical reactions.

32. Protein Processing • The proteins produced by cells have many uses • Proteins sent outside the cell must be kept separate from the rest of the cytoplasm. • This is achieved by the cell by packaging the proteins in vesicles. • Vesicles--is a small cavity or sac that contains materials in a eukaryotic cell.

33. In a eukaryotic cell, two structures are responsible for modifying, packaging, and transporting proteins for outside the cell. • The endoplasmic reticulum and the Golgi apparatus are organelles that prepare proteins for extracellular export.

34. Endoplasmic Reticulum--it is a system of membranes that is found in a cell’s cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids. • Rough ER--ribosomes are attached to some parts of the surface of the ER. As proteins are made they cross the ER membrane, entering the ER. The ER membrane then pinches off to form a vesicle around the proteins. • Smooth ER--this has no attached ribosomes. Enzymes of the smooth ER performs various functions, such as making lipids and breaking down toxic substances.

35. Golgi Apparatus—a cell organelle that helps make and package materials to be transported out of the cell. • Repackaging--vesicles that contain newly made proteins move through the cytoplasm from the ER to the Golgi apparatus. • Inside the Golgi apparatus, enzymes modify the proteins as they move through the organelle. • On the other side, the finished proteins are enclosed in new vesicles that bud from the surface of the Golgi apparatus.

36. Exporting--many of these vesicles then migrate to the cell membrane. As the vesicle membrane fuses with the cell membrane, the completed proteins are released to the outside the cell.

37. Storage and Maintenance • Vesicles help maintain homeostasis by storing and releasing various substances as the cell needs them. • Lysosome—this is a vesicle that contains specific enzymes that break down large molecules. These enzymes can digest food particles to provide nutrients for the cell. • They recycle materials in the cell by digesting old, damaged, or unused organelles. • Lysosomes made by the Golgi apparatus, prevent enzymes from destroying the cell.

38. Central Vacuole—a vacuole is a fluid filled vesicle found in the cytoplasm of plant cells or protists. • This large vacuole stores water, ions, nutrients, and wastes. • Can also store toxins or pigments. • When filled with water it makes the cell rigid, allowing the plant to stand up straight. When the vacuole loses water the cell shrinks and the plant wilts.

40. Other Vacuoles--some protists have contractile vacuoles, which pump excess water out of the cell. This process controls the concentration of salts and other molecules and helps the cell maintain homeostasis. • Another vacuoles forms when the cell membrane surrounds food particles outside the cell and pinches off to form a vesicle inside the cell. • When a food vacuole later fuses with a lysosome, the enzymes that digest the stored food are released.

41. Energy Production • Cells need a constant source of energy. • The energy for cellular functions is produced by chemical reactions that occur in the mitochondria and chloroplasts. • Nearly all eukaryotic cells contain mitochondria. • Chloroplasts are found in plants and some plant like protists, like seaweed, but it is not found in animal cells.

42. In both organelles, chemical reactions produce adenosine triphosphate (ATP), the form of energy that fuels almost all cell processes.

43. Chloroplasts--an organelle found in plant and algae cells where photosynthesis. • It uses light energy to make sugar from carbon dioxide and water. • Each chloroplasts are surrounded by stacks of flattened sacs. The ATP-producing chemical reactions take place on the membranes of these sacs.

44. Mitochondria—in eukaryotic cells, the cell organelle that is surrounded by two membranes and that is the site of cellular respiration. • It uses energy from organic compounds to make ATP. • Some ATP is made in the cytosol, most of a cell’s ATP is made inside the mitochondria. • Cells that have a high energy requirement, such as muscle cells, may contain hundreds or thousands of mitochondria. • Has a smooth outer membrane and a folded inner membrane. • Many ATP-producing enzymes are located on the inner membrane,

45. In what kinds of cells are mitochondria found? • In nearly all eukaryotic cells, including plant cells, contain mitochondria.

46. From Cells to OrganismSection 3 • Why it matters—diverse organisms have unique cells and cellular organization.

47. More than 50 million types of organisms live on Earth. Each organism is made up of different types of cells. Differences in cells enable organisms to adapt to their natural environments.

48. Diversity in Cells • Prokaryotes are always unicellular and limited in size. • They lack a nucleus and membrane bound organelles • They come in a variety of shapes and structures. • Eukaryotes are can be unicellular or multicellular and usually larger than prokaryotes. • They have a nucleus and membrane bound organelles. • Come in a variety of shapes and structures.

49. Remember cell’s shape reflects its function. • The different organelles and features of cells enable organisms to function in unique ways in different environments.

50. Diversity in prokaryotes: • Can vary in shape, they way they obtain and use energy, the make-up of their cell walls, and their ability to move. • Many have flagella. • Flagella--a long hair like structure that grows out of a cell and enables the cell to move. • Many have pili. These are short, thick outgrowths that allow the prokaryotes to attach to surfaces or other cells.